It is known that ceramic materials can be synthesized by spray-drying mixed aqueous solutions of salts of the desired metallic constituents, pressing the resulting homogeneous powder into a compact, and sintering. The products of this process are non-uniform porous structures, however, because the as-formed powder cannot be cold compacted, in the green state, to a level of densification sufficiently high for subsequent high temperature sintering to be effective. Reducing the particle size of the initially-formed powder mechanically prior to compaction and sintering leads to only marginal improvements in the final product.
Although such non-uniform porous materials are acceptable for certain purposes, it is highly desirable in many applications to have structurally and compositionally uniform, low porosity, fine grain ceramic materials. An example of a type of ceramic requiring such properties is manganese-zinc ferrite for use in magnetic suspensions.
Manganese-zinc ferrites for magnetic applications should have minimum spatial and time-dependent variations in permeability, and should be mechanically strong to resist damage during machining and assembly of parts. As spatial permeability variation results from small variations in microstructure and from mechanically-induced defects, minimization of such variations requires uniform fine grain microstructures. Time dependent changes in permeability depend on ferrite chemistry, therefore necessitating compositional uniformity for time-stable materials. Mechanical strength for a given chemistry depends on the level of densification and on grain size achieved during sintering.
Many other applications also require ceramic materials having superior compositional and structural uniformity, fine grain size, and high strength. This need is met in the present invention.